Most therapeutic proteins bind to a single target protein with high specificity, thereby interfering with the activity of this single target protein. That protein may be a part of one or more biological pathways that mediate a human disease being treated, and the therapeutic protein may therefore inhibit disease progression. However, efficacy of therapeutic proteins is rarely complete for all patients. Incomplete efficacy of therapeutic proteins could be due in some cases to the complexity of a disease. For example, some diseases may be mediated by multiple biological pathways, or different biological pathways may play a predominant role in mediating disease activity in different patients having the same clinically-defined condition. Hence, in some diseases it may be advantageous to simultaneously inhibit at least two biological pathways.